I have a table with column Catchment area (in km2), and I need to set symbol diameter based on that column. I need to get .sld file so I'm working with uDig but if you know better software for this, I will accept your advice.

EDIT:
I found out how to do it, but result is not acceptable because symbols are too big. There is no any normalization option in uDig or QGIS.

Can you explain more detailed what I need to do? How to use the square root or normalization in QGIS?
– againstflowOct 16 '11 at 12:43

I did normalization of symbol size in ArcMap, but there is not option to save .sld. So I installed Arc2Earth and exported style like .sld, but in uDig it can't be read, says it is an error. Geoserver won't show that style so it's not correct. Is there an option to import .sld in QGIS?
– againstflowOct 16 '11 at 13:01

No, there is no SLD import as far as I know.
– underdark♦Feb 14 '12 at 20:09